Various complexes containing two, three and four chromium atoms are known. With respect to bi- and trinuclear chromium complexes, see, for example, Magneto-Structural Correlation in Exchange Coupled Systems, Willett et al., Ridel, Dordrecht, pp. 497-522 (1985). See also Dubicki et al., Inorganic Chemistry, 11, 1869 (1972) and Figgis et al., Nature (London), 205, 694 (1964) who report a trinuclear chromium (III) acetate in which the three chromium atoms are linked to a central oxygen atom.
Two complexes of chromium that have four chromium atoms bound to a central sulfur atom have been reported in journal articles. For instance, Darensburg et al., Organometallics, 3, 1598-1600 (1984) report the synthesis of a sulfur-capped trinuclear chromium carbonyl cluster, S[Cr(CO).sub.4 ].sub.3.sup.2- ; and Hoefler et al., J. Am. Chem. Soc., 105, 6338-6339 (1983) report the synthesis of [PPN].sub.2 (.mu..sub.2 -CO).sub.3 (CO).sub.9 Cr.sub.3 (.mu..sub.4- S)Cr(CO).sub.5 ], in which the anion consists of chromium triangle capped with an SCr(CO).sub.5 group.
Chromium complexes with bridging ligands formed from benzoic acid and containing three chromium atoms connected to a central sulfur atom have been reported by Eremenko et al., Inorg. Chim. Acta, 73, 225-229 (1983).
None of these references disclose a tetranuclear sulfide bridged complex of Cr (III). Accordingly, the invention embodied herein is believed by the applicants to be novel in all its aspects.